This study presents the synthesis and optical properties of a new class of bright green-yellow fluorescent dyes with potential applications in bioimaging. A facile synthetic route via the chelation of aryl(hetaryl)aminoacryloylthiophene scaffolds with a BF2 fragment is presented. The photophysical properties of the dyes are attributed to the nature and position of electron-donating and electron-withdrawing substituents. Upon coordination to a BF2 fragment, characteristic emission was observed, with λem ranging from 503 to 543 nm and quantum yields of 0.14-0.42. Compared with parent aryl(hetaryl)aminoacryloylthiophenes, a significant red shift in absorption (up to 480 nm in solution) and emission (up to 543 nm in solution and 610 nm in the solid state) and high chemical stability and photostability were observed. The electron-accepting character of the substituents on the terminal aromatic ring or replacing this fragment with pyridine or pyrazine moieties resulted in increased quantum yields. To gain insight into the electronic structures and optical properties, quantum mechanical calculations were performed. The results of (TD-)DFT calculations supported the structural and spectroscopic data and showed the features of electronic distribution in the frontier molecular orbitals and active electrophilic and nucleophilic sites in the compounds investigated. Synthesized BF2 complexes are promising dyes for cell imaging and flow cytometry owing to their ready penetration and accumulation in cells.
An efficient synthesis of a new series of di‐ and trisubstituted thiazoles (TZs) bearing aryl enamine side‐chains (ETZs) has been developed and the optical properties of these compounds compared with structural analogues containing the isoelectronic aza‐enamine group (ATZs). Spectral characterization demonstrated the difference in the absorption and fluorescence of the ETZs and ATZs in solution and the emergence of fluorescent ETZs in the solid state. The optimized structural geometries and weak intramolecular interactions, electronic characteristics of the ground and excited states, HOMO and LUMO analyses, changes in electron density after S0 → S1v excitation and maps of electrostatic potential (MEPs) calculated by means of DFT have allowed us to estimate the particularities of the geometric and electronic structures of the ETZs and ATZs in the ground and excited states. The availability, synthetic simplicity, stability, large Stokes shifts and high sensitivity to the microenvironment (fluorosolvatochromic behaviour) make the obtained TZs a useful platform for the further design and synthesis of new effective compounds for applications in the field of fluorescence imaging.
A highly
efficient approach to a new class of polycyclic 8-azapurines,
benzo[4,5]imidazo[1,2-a][1,2,3]triazolo[4,5-e]pyrimidines (BITPs), with good photophysical characteristics
is proposed. The approach comprises condensation of aminobenzimidazoles
with 3-oxo-2-phenylazopropionitrile to form 3-(arylazo)benzo[4,5]imidazo[1,2-a]pyrimidine-4-amines, which undergo oxidative cyclization
by the catalytic action of copper(II) acetate, resulting in BITPs
with 73–84% yield. Spectral investigations demonstrated the
fluorescent properties of BITPs, exhibiting good quantum yields (up
to 60%) with maxima absorption at 379–399 and emission at 471–505
nm.
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